Escrow Account Management

[sangier]

• Research how to manage escrow account

• Implement escrow account management.

• Serdar comment: Right now, we don't have an escrow, but the app should work good enough for testing.

[srdtrk]

We might want to go in the direction of yui-ibc-solidity and introduce an escrow contract (similar to bank keeper). Thanks for this suggestion @gjermundgaraba. This would help with:

1. Migration: Right now, all escrow tokens are held by ICS20Transfer.sol. Since we plan to introduce migrations via proxy contracts in [EPIC] Support migrations and recoveries in IBC contracts #12, it would make more sense for there to be a separate escrow manager contract that manages the escrow. This way, we can migrate ICS20 without moving the escrowed funds.

2. Modularity: Right now, ICS20Transfer.sol handles the conversions between ERC20 and SdkCoin via the SdkCoin.sol library. This is not ideal since this ICS20Transfer.sol implementation would only be usable between ERC20 and Cosmos. It might make more sense to move this layer to the escrow contract. But this still needs more research.